Manufacturers and designers have invested tremendously on the research and development of dual-band or tri-band dipole antennas for WiMAX/WLAN, and some of the research results are disclosed in the following patents and patent applications: (1) R.O.C. Pat. No. 1283945 entitled “Dual-band dipole antenna”, (2) R.O.C. Pat. Publication No. 200727533 entitled “Planar dipole antenna”, (3) R.O.C. Pat. Publication No. 200701556 entitled “Dual-band dipole antenna”, (4) R.O.C. Pat. Publication No. 200719532 entitled “Dipole antenna”, (5) U.K. Pat. Application No. 0518996.4 entitled “Balanced antenna devices” and (6) U.S. Pat Application No. [2005/0035919A1] of application Ser. No. 10/641,913 entitled “Multi-band printed dipole antenna”.
However, the aforementioned patents (1), (2) and (3) achieve their functions by a more complicated structure, a heavier weight and a higher cost, and a more difficult way of integrating a radio frequency circuit system. The aforementioned patents (4), (5) and (6) can be operated by a wideband or dual-band antennas only. On the other hand, a printed structure of the present invention comes with a light weight, a low profile, a low cost and an easy way of integrating a radio frequency circuit system.